The only thing Friday night’s 95-92 loss to the New Orleans Pelicans proved was that the Celtics remain unable to close out games, as evidenced by three painful home losses over the past two weeks.

The Celtics’ home-heavy December schedule was supposed to allow them to rack up some victories in preparation for their biggest road test in Brad Stevens’s first season as coach. On Sunday at Oklahoma City, the Celtics begin an arduous and challenging five-game road trip that will see them as underdogs the entire journey.

The trip continues Tuesday in Denver, and then takes the Celtics to Los Angeles Wednesday for a rematch with Doc Rivers and the Clippers, before ending with perhaps the most difficult back-to-back in the league — Friday at Golden State and Saturday at Portland. This undertaking is waiting for a team that’s lost six of seven games, including three in a row.

The Celtics spent a short time in first place in the Atlantic Division a few weeks ago, but now live among the also-rans in the division, just a few games ahead of the Brooklyn Nets and New York Knicks.

A winless trip could change the complexion of Boston’s season. It may turn from a transition season to a rebuilding season. At 13-20, the Celtics’ season could be determined over the next week, and that point is not lost on the players.

“I’m excited, this is why I play this game,” said shooting guard Avery Bradley. “To play against those great teams like that. We get a chance to go out there and prove ourselves.”

The Celtics were hoping to enter this trip with some momentum, but they wasted a couple of opportunities to steal one Friday against the Pelicans with two missed shots in the final 10 seconds.

The Celtics were 4-for-26 shooting in the fourth quarter, including 0 for 7 from Jared Sullinger, who is nursing a badly bruised left hand that is affecting his touch around the basket.

Of course, the five teams set to face the Celtics will have little sympathy for their issues. The Thunder are playing without Russell Westbrook, who is missing his second stint of time because of knee surgery. Oklahoma City has also lost two consecutive home games, including Thursday’s stunning loss to the Nets on a last-second shot by Joe Johnson.

The Nuggets snapped an eight-game losing streak Friday with a win over Memphis, while the Clippers will be playing without Chris Paul, who separated his right shoulder Friday at Dallas. The Warriors and Blazers are among the toughest home teams in the NBA.

“Every road trip is a make or break, especially with the situation we are in where we’ve lost a couple of games in a row,” he said. “So we’re going out on a West Coast trip, playing some pretty good teams, so this could send us in the right direction as far as where we want to go in our season or kind of destroy our whole season. Guys are going to have to pull together. We’re going to have to become as one on the road and we’re going to have some tough battles.”

Several Celtics refused to look at this difficult road swing as anything but an opportunity.

“I don’t want to speak for the team but I’m excited for the road trip,” guard Jordan Crawford said. “It’s very challenging games coming up and we’ve been playing well, shots just haven’t been falling some games. But we’ve been doing a lot of positive things.”

Said Sullinger: “I’m very excited to go on the road, try to get some more wins. We let two slide by us for the past few days and we’ve got to try to get on the road and steal some.”

Stevens continues to stress development and progress over actual victories, and he said he was pleased with the way his club has been playing, despite the losing skid. The Celtics are shooting 39.9 percent in their last five games. They have experienced disturbing scoring droughts throughout the season, and if they hope to steal a win or two during this trip and remain in playoff contention, Stevens said they must shore up their weaknesses.

“I know our guys are looking forward to going and competing,” Stevens said. “We play five really good teams on the trip and then we play a really good team when we get back [Houston]. It’s just never going to stop, we just have to continue to play better ourselves.”